Divergent impacts of antibiotics on ferrihydrite biotransformation by Shewanella oneidensis: electron transfer regulation and iron redox cycling

Abstract

Antibiotics, as ubiquitous environmental pollutants, disrupt iron biogeochemical cycles. However, their role in regulating ferrihydrite (Fh) transformation mediated by dissimilatory iron-reducing bacteria, and their coupled conversion, remains poorly understood. This study investigates the influence of antibiotics on Fh biotransformation by Shewanella oneidensis MR-1, focusing on the regulation of microbe–mineral interfacial electron transfer. Among seven representative antibiotics, sulfamethoxazole enhanced Fe(II) production by promoting microbial electron flux, thereby accelerating Fh transformation toward magnetite. Conversely, chloramphenicol suppressed Fe(II) generation by competing for microbial electrons via nitro group reduction and inhibiting extracellular electron transfer, kinetically trapping mineral transformation at the goethite stage. Sulfamethoxazole was reductively degraded by biogenic Fe(II) via N–O bond cleavage, facilitating green rust formation and further promoting magnetite nucleation, whereas chloramphenicol was predominantly hydrolyzed by microbes or on mineral surfaces without contributing to Fe(III) reduction. These findings reveal that antibiotics can serve as either electron mediators or competitors, directly coupling their degradation to iron redox cycling and controlling mineral transformation pathways. This work provides novel insights into the environmental persistence of antibiotics and their previously overlooked role in mineral transformation, with critical implications for managing antibiotic-contaminated ecosystems.